Designers of next generation vehicles of all types are striving to design lighter, smaller, and easier to repair vehicles. To accomplish these goals the communication systems within the vehicles must also be lighter, smaller, and easier to repair. One way to achieve these goals in systems with multiple radio communication means is to have multiple transmitters and receivers operate over the same antenna. Combining multiple transmitters and receivers onto a single antenna reduces the number of antennas that need to be placed on the vehicle without sacrificing functionality. The combination also leads to integration of electronics, which reduces the size, weight, and number of components of the system. Combining multiple transmitters and receivers onto a single antenna, however, presents its own difficulties, especially when the transmitters and receivers operate within the same frequency band.
Currently, there are conventional devices which transmit and receive simultaneously on different channels in separate frequency bands over a single antenna. These conventional devices accomplish this by separating the transmit and receive frequency bands with many megahertz of bandwidth. Because the transmit and receive frequency bands are so separated, conventional filters can be used to separate the receive frequencies from the transmit frequencies.
In some communication systems, however, combining transmitters and receivers is not so easy. For example, in some aircraft communication systems, the radios transmit and receive on the same frequency, as in a push-to-talk type system. Additionally, there are multiple transmitters (and receivers) that operate within the same frequency band. In this situation, a conventional system cannot filter out a transmitted signal on a first channel from a received signal on a second channel within the same frequency band, because the transmitted signal and the receive signal are so near in frequency. The transmitted signal is of a higher power than the received signal and it saturates any active signal processing elements and masks any signals received on the second channel. Thus, connecting multiple transmitters and receivers to a single antenna in a conventional system does not allow simultaneous use of transmitters and receivers of different channels within the same frequency band. When the communications systems require independent simultaneous use of two transmitters or two receivers, simply connecting multiple transmitters and receivers to an antenna is unacceptable.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an apparatus and method for simultaneously transmitting and receiving multiple radio signals within the same frequency band over a single antenna.